Flameless heating system

ABSTRACT

A mobile heating system is disclosed. In one embodiment, the system includes an enclosure defining a plenum that houses a fan and an internal combustion engine. The heating system also includes a hydraulic circuit including a hydraulic pump operably coupled to the internal combustion engine and a first heat exchanger located in the plenum and in fluid communication with the hydraulic pump. The hydraulic circuit also includes a hydraulic motor operably coupled to the fan wherein the hydraulic motor is in fluid communication with and driven by the hydraulic pump. A first valve is disposed between the hydraulic pump and the heat exchanger and is configured to restrict fluid flow and to increase a fluid pumping pressure of the hydraulic pump. A second valve is located upstream of the first valve and is configured to selectively direct hydraulic fluid between the first valve and the hydraulic motor.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No.14/951,021, filed on Nov. 24, 2015, which is a Continuation of U.S.patent application Ser. No. 13/458,489, U.S. Pat. No. 9,228,760, filedon Apr. 27, 2012, issued on Jan. 5, 2016, entitled FLAMELESS HEATINGSYSTEM, the disclosures of which are hereby incorporated by reference intheir entireties.

BACKGROUND

Industrial heaters are used in a wide variety of situations, includingoutdoor construction, oil drilling, airports, unheated buildings, etc.Most industrial heaters utilize an internal combustion engine along witha combustion-type generator or burner which uses a flame to produceheat. However, in some instances, such as oil wells, a flame cannot beused to produce the heat due to safety concerns. In such instances,flameless heaters have been developed. However, improvements inflameless heater technology are desired, particularly with regard toefficiency.

SUMMARY

A mobile heating system is disclosed. In one embodiment, the systemincludes an enclosure supported by a mobile chassis wherein theenclosure defines an air plenum having an air inlet and an air outlet.The system also includes a fan disposed in the air plenum wherein thefan is configured to move an air flow stream from the air inlet to theair outlet of the enclosure. An internal combustion engine is alsodisposed in the air plenum. The heating system also includes a hydrauliccircuit including a hydraulic pump operably coupled to the output shaftof the internal combustion engine, and a first heat exchanger located inthe enclosure air plenum and in fluid communication with the hydraulicpump. The first heat exchanger is configured to transfer heat from fluidin the hydraulic circuit to the air flow stream. The hydraulic circuitalso includes a hydraulic motor operably coupled to the fan wherein thehydraulic motor is in fluid communication with and driven by thehydraulic pump. A first valve is disposed between the hydraulic pump andthe heat exchanger and is configured to restrict fluid flow and toincrease a fluid pumping pressure of the hydraulic pump. A second valveis located upstream of the first valve and is configured to selectivelydirect hydraulic fluid between the first valve and the hydraulic motor.In one embodiment, the system further includes a control systemconfigured to operate the second valve to maintain a temperature setpoint of the air flow stream.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments are described with referenceto the following figures, which are not necessarily drawn to scale,wherein like reference numerals refer to like parts throughout thevarious views unless otherwise specified.

FIG. 1 is a schematic view of a flameless heating system having featuresthat are examples of aspects in accordance with the principles of thepresent disclosure.

FIG. 2 is a schematic view of a control system usable with the flamelessheating system shown in FIG. 1.

FIG. 2A is a screenshot of a user interface suitable for use with thecontrol system shown FIG. 2 wherein the interface shows an automaticmode of operation.

FIG. 2B is a screenshot of a user interface suitable for use with thecontrol system shown FIG. 2 wherein the interface shows a manual mode ofoperation.

FIG. 3 is a perspective view of a hydraulic manifold usable with theflameless heating system shown in FIG. 1.

FIG. 3A is a perspective view of the hydraulic manifold of FIG. 3 withan altered porting arrangement.

FIG. 4 is a first side view of the hydraulic manifold shown in FIG. 3.

FIG. 5 is a second side view of the hydraulic manifold shown in FIG. 3.

FIG. 6 is a third side view of the hydraulic manifold shown in FIG. 3.

FIG. 7 is a fourth side view of the hydraulic manifold shown in FIG. 3.

FIG. 8 is a fifth side view of the hydraulic manifold shown in FIG. 3.

FIG. 9 is a sixth side view of the hydraulic manifold shown in FIG. 3.

FIG. 10 is a front perspective view of an exhaust heat exchanger usablewith the flameless heater of FIG. 1.

FIG. 11 is a rear perspective view of the exhaust heat exchanger shownin FIG. 10

FIG. 12 is a schematic cross-section of the exhaust heat exchanger shownin FIG. 10 taken along the line 12-12.

FIG. 13 is a side view of an exemplary physical embodiment of theflameless heating system shown in FIG. 1.

DETAILED DESCRIPTION

Various embodiments will be described in detail with reference to thedrawings, wherein like reference numerals represent like parts andassemblies throughout the several views. Reference to variousembodiments does not limit the scope of the claims attached hereto.Additionally, any examples set forth in this specification are notintended to be limiting and merely set forth some of the many possibleembodiments for the appended claims.

Referring to FIG. 1, a flameless heating system 10 is shown. Flamelessheating system 10 is for heating an airflow stream 32. As shown,flameless heating system 10 has an interior plenum 20 defined by ahousing 22. At one end of the housing 22, an ambient air intake 24 isprovided for receiving an ambient airflow stream 32 a. At another end ofthe housing 22, a heated air outlet 26 is provided for discharging theheated airflow stream 32 b. Referring to FIG. 13, flameless heatingsystem 10 includes a chassis 12 to which wheels 14 are rotatablymounted. Flameless heating system 10 may also include a hitch 16 suchthat the system 10 may be towed by a vehicle. Alternatively, flamelessheating system 10 may be skid mounted or mounted onto or within avehicle. Accordingly, flameless heating system 10 is a mobile heatingsystem.

A fan 30 is also provided to move air from the intake 24, through theplenum 20, and out of the outlet 26. In one embodiment, the fan 30 isconfigured to provide up to 1,200 cubic feet per minute (cfm) of airflow at 5 inches total static pressure. However, it should beappreciated that fan 30 can be configured with a higher or lower airflowcapacity depending upon application and arrangement. A bulkhead 28 mayalso be provided to ensure air flowing through the plenum 20 issufficiently drawn through and/or across the internal componentsresponsible for heating the airflow stream 32 a. As shown, a temperaturesensor T1 is provided downstream of fan 30 near the outlet 26 formeasuring the temperature of the heated airflow stream 32 b.

Within the housing, an internal combustion engine 100 is provided. Asshown, internal combustion engine 100 has an output shaft 102 fordriving a hydraulic pump 204, discussed later. In one embodiment, theinternal combustion engine 100 is configured to provide an outputcapacity of 25 horsepower at 2,500 revolutions per minute (rpm). In oneembodiment, the internal combustion engine is a water-cooled dieselengine with a displacement of 1.5 liters. However, internal combustionengine 100 can also be provided with other output capacities, asdesired. It is noted that internal combustion engine could be configuredto burn other fuels, such as gasoline and ethanol. When the internalcombustion engine 100 is operating, radiation from the surface of theengine 100 provides heating to the plenum 20. In one embodiment,operation of the internal combustion engine 100 results in heatradiation to the plenum 20 of about 18,000 British Thermal Units perhour (BTU/hour).

A fuel tank 104, a fuel line 106, and a fuel pump 114 are also providedfor delivering fuel to the internal combustion engine 100. In oneembodiment, the fuel pump 114 is configured to deliver about 1.8 gallonsper hour (gph) to the internal combustion engine 100.

In one embodiment, the internal combustion engine 100 is cooled by aradiator or heat exchanger 108 via coolant lines 110 and 112. As shown,the radiator 108 is arranged within plenum 20 such that the radiator 108may be used to heat the airflow stream 32. In one embodiment, thetemperature of the incoming coolant line is about 180 degrees F. whilethe temperature of the outgoing coolant line 110 is about 170 degrees F.at a coolant flow rate of about 14 gallons per minute. In such anembodiment, approximately 64,000 BTU/hour of heat can be transferred tothe plenum 20 from the radiator 108.

The combustion exhaust from the engine 100 is connected to a heatexchanger 120 via piping 116, both of which are disposed in the plenum20 such that they may heat the airflow stream 32. After flowing throughthe heat exchanger 120, the exhaust is routed to atmosphere via exhaustpipe 118. Referring to FIGS. 10 and 11, an exemplary physicalarrangement of a heat exchanger 120 is shown. In the embodiment shown,heat exchanger 120 includes an inlet 122 for receiving exhaust from pipe116 and an outlet 124 for discharging exhaust to pipe 118. In oneembodiment, an additional exhaust pipe 118 is not utilized and outlet124 serves as the final discharge point for exhaust to the atmosphere.Between the inlet 122 and the outlet 124 is tubing 132 that is exposedto the airflow stream 32. As shown, the tubing 132 has a nominaldiameter of about 2 inches and a length of about 15 feet. In theembodiment shown, tubing 132 is provided in a single pass serpentinearrangement with four complete loops such that the length of the tubing132 can be extended for greater heat transfer capacity.

As most easily seen at FIG. 12, tubing 132 has nine straight tubesections 132 a, each of which is offset from an adjacent section 132 aby a distance X in a first direction 136 and by a distance Y in a seconddirection 138. In one embodiment distance X is about 6 inches anddistance Y is about 5 inches. This configuration allows for a compactheat exchanger in which each straight tube section 132 a is directlyexposed to the airflow stream 32 without interference from the adjacentstraight tube sections 132 a. This feature is also beneficial forimproving heat transfer. It is noted that more or fewer loops andcorresponding straight sections may be utilized depending uponapplication and desired heat transfer characteristics. Additionally, theoffset distances X and Y may be similarly adjusted.

Between the tubing 132 and the outlet 124 is an engine muffler 134 forattenuating the sound output of the flameless heating system 10. As themuffler 134 is also exposed to the airflow stream 32, additional heattransfer is made possible. As shown, the tubing 132 and the muffler 134are supported by a frame 126, a first support 128 and a second support130. As configured, the disclosed exhaust heat exchanger 120 cantransfer approximately 26,000 BTU/hour to airflow stream 32 flowing atapproximately 1,200 cubic feet per minute when the exhaust temperatureis about 1000 degrees F.

Referring back to FIG. 1, the flameless heating system 10 furtherincludes a hydraulic system 200. Hydraulic system 200 is for convertingthe rotational energy provided by the internal combustion engine 100 tothermal energy that can be used to increase the temperature of theairflow stream 32 through the use of a hydraulic fluid. One example of ahydraulic fluid usable in hydraulic system 200 is hydraulic transmissionfluid (HTF).

The primary components of the hydraulic system 200 are a pump 204, aheat exchanger 220, a hydraulic motor 216, and a hydraulic fluid storagetank 202. A number of valves are also provided in hydraulic system 200for selectively heating and/or distributing the hydraulic fluid amongthe primary components. In one embodiment, the valves are provided in amanifold 290. Each of these features of the hydraulic system isdiscussed in further detail below.

As shown, hydraulic system 200 includes a hydraulic pump 204mechanically coupled to and driven by the output shaft 102 of theinternal combustion engine 100. In one embodiment, the pump 204 isdirectly connected to the output shaft 102. In one embodiment, the pump204 is coupled to the output shaft 102 with a belt, gears, or splineoutput shaft. In one embodiment, the hydraulic pump 204 is an axialpiston pump which may have a variable or fixed displacement. Other typesof pumps may be used. In one embodiment, the internal combustion engine100 and the hydraulic pump 204 are configured to provide a flow rate ofabout 28 gallons per minute of hydraulic fluid. However, it should beunderstood that pump 204 can be configured to provide any desired flowamount.

In the embodiment shown, the hydraulic pump 204 is configured to performtwo primary functions. A first function of the hydraulic pump 204 is todeliver hydraulic fluid to the heat exchanger 220 and to the hydraulicmotor 216. A second function of the hydraulic pump 204 is to heat thehydraulic fluid by imparting kinetic energy into the fluid. A firstvalve 206, discussed in more detail later, is located downstream of thepump 204 to provide resistance to the hydraulic pump 204 for thispurpose. The corresponding pressure drop through the first valve 206results in the primary heating of the hydraulic fluid as it passesthrough the valve 206.

As shown, the inlet of the pump 204 is connected to the storage tank 202via a branch line 250. The storage tank 202 is oriented (e.g. elevatedabove the pump) to ensure that the pump 204 has sufficient head pressuresufficient to avoid pump cavitation and also adds volume to the systemwhich helps to reduce the concentration of potential contaminants in thehydraulic fluid. In the embodiment shown, a temperature sensor T2 isprovided in the storage tank 202 to sense the stored hydraulic fluid.

The discharge side of the pump 204 is most directly in fluidcommunication with a second valve 208 (via branches 252, 254) and with athird valve 210 (via branches 252, 258). As shown, the second valve 208is a two-way control valve with an actuator 208 a to operate the valvebetween an open position and a closed position. In one embodiment, thesecond valve 208 is an electro-hydraulic, proportional, in-line type,pressure compensated, hydraulic flow control valve. It is noted thatsecond valve 208 is optional to the flameless heating system 10, and insome embodiments it is preferred to configure the system 10 withoutvalve 208 and branch lines 254, 256.

When in the open position, the second valve 208 allows the flamelessheating system 10 to be placed in a warm-up mode. In the warm-up modehydraulic fluid is heated with minimal loading the engine via a warm-upflow path (branches 256, 276) to the heat exchanger 220 that bypassesthe first valve 206. This operation is beneficial during engine warm-upwhere premature loading of the engine may be harmful. Once the enginesystem and hydraulic fluid have been warmed sufficiently, the secondvalve 208 can be moved to the closed position thereby forcing hydraulicfluid into branch 258 and eventually to the first valve 206.

When the second valve 208 is in the closed position, the third valve 210operates to protect the system from over-pressurization. In theembodiment shown, the third valve 210 is a pressure relief type valve.As configured, the third valve 210 is a fail-safe component thatfunctions to bleed off excess pressure back to the tank 202, therebyeliminating harm to the hydraulic system 200 and its components. Forexample, the third valve 210 can have a setting of 1,750 psi to ensurethe hydraulic fluid pressure, at the location of the third valve 210,never exceeds this value.

A fourth valve 212 is provided downstream of the third valve 210 viabranch line 260. The fourth valve 212 is for selectively providing fluidto the first valve 206 and/or to the hydraulic motor 216. In theembodiment shown, the fourth valve 212 is a bypass-type flow controlvalve having an actuator 212 a that can selectively deliver fluidbetween branches 262 and 264. Branch 262 leads directly to the hydraulicmotor 216 while branch 264 leads to the first valve 206 via branch 270and to a fifth valve via branch 266. A pressure sensor is provided inbranch line 260 to measure the hydraulic fluid pressure between thefourth valve 212 and the third valve 210.

The hydraulic motor 216 is mechanically coupled to fan 30, andpreferably located in the plenum 20 downstream of the heat exchangers108, 220, and 120. However, hydraulic motor 216 and fan 30 may belocated in a different portion of the plenum 20. Hydraulic motor 216 mayalso be located entirely outside of the airflow stream 32 as well.Hydraulic motor 216 may be directly coupled to the fan 30 or may becoupled to the fan 30 via belts or gears. Hydraulic fluid leaving themotor 216 is filtered via filter 218 and returned to the storage tankvia branches 280 and 282. It is noted that the hydraulic motor 216further heats the hydraulic fluid as the pressure in the fluid isdecreased by the hydraulic motor 216. In one embodiment, the hydraulicmotor 216 is configured to operate with a flow of about 4 to about 6gallons per minute (gpm), for example about 5 gpm. However, it is notedthat hydraulic motor 216 could be configured to operate at any desiredflow rate.

The fifth valve 214 is placed in a parallel arrangement with the firstvalve 206 such that hydraulic fluid may be bypassed around the firstvalve 206 while still allowing for hydraulic fluid to flow to thehydraulic motor 216. As shown, the fifth valve 214 is a two-way controlvalve having an actuator 214 a to operate the valve between an openposition and a closed position. In one embodiment, the fifth valve 214is an electro-hydraulic, proportional, in-line type, pressurecompensated, hydraulic flow control valve.

As configured, the fifth valve 214 is in a normally closed state duringregular operation of the flameless heating system 10 such that hydraulicfluid must pass through the first valve 206. When heating is no longerdesired, the fifth valve 214 may be opened to place the system in acool-down mode wherein hydraulic fluid is allowed to bypass the firstvalve 206 and unload the pump 204. Accordingly, with the fifth valve 214in the open position, hydraulic fluid can flow directly to the heatexchanger 220 (via branches 268, 274, 276) without being heated by thefirst valve 206. Because the hydraulic motor 216 still receiveshydraulic fluid when the fifth valve 214 is open (assuming the secondvalve 208 is closed), the temperature of the hydraulic fluid can bequickly dissipated as it passes through the heat exchanger 220 with thefan 30 operating. It is noted that the fifth valve 214 is optional tothe flameless heating system 10, and in some embodiments it is preferredto configure the system 10 without valve 214 and branch lines 256, 268.

When both the second valve 208 and the fifth valve 214 are both closed,the hydraulic fluid will flow through the first valve 206. In theembodiment shown, the first valve 206 is a pressure relief type valve ora regulator type valve having an actuator 206 a. As shown, the fifthvalve is controllable to selectively reduce the pressure of thehydraulic fluid such that a desired output is achieved. As the hydraulicfluid passes through the first valve 206 and the pressure of the fluidis reduced, for example from 1,500 psi down to 100 psi, the hydraulicfluid temperature is further increased. After passing through the firstvalve 206, the hydraulic fluid is delivered to the heat exchanger 220via branches 272, 274, and 276. The heat exchanger 220 is located in theplenum 20 downstream of the internal combustion engine and upstream ofthe engine exhaust heat exchanger. In one embodiment, the heat exchanger220 is a bar and plate heat exchanger. Hydraulic fluid leaving the heatexchanger 220 is returned to the storage tank 202 and filtered viabranch lines 278 and 282 and filter 218, respectively.

Referring to FIGS. 3-9, the manifold block 290 is shown in greaterdetail. As shown, manifold block 290 has a first side 290 a, a secondside 290 b, a third side 290 c, a fourth side 290 d, a fifth side 290 e,and a sixth side 290 f. On the first side 290 a, ports for the valves206, 210, and 212 are provided. On the second side 290 b, ports forvalve 208, valve 214, and branch line 260 are provided. On the thirdside 290 c, ports for branch lines 252 and 276 are provided. On thefourth side 290 d, ports for branch lines 280 and 262 are provided. Asconfigured, the manifold block 290 is adapted to receive and retain theactuators 206 a, 208 a, 212 a, 214 a for each respective valve and port.FIG. 3A shows the same manifold block 290, but with a slightly differentporting arrangement on the third side 290 c.

Referring to FIG. 2, the flameless heating system 10 may also include anelectronic controller 50. The electronic controller 50 is schematicallyshown as including a processor 50A and a non-transient storage medium ormemory 50B, such as RAM, flash drive or a hard drive. Memory 50B is forstoring executable code, the operating parameters, and the input fromthe operator user interface 52 while processor 50A is for executing thecode.

The electronic controller 50 typically includes at least some form ofmemory 50B. Examples of memory 50B include computer readable media.Computer readable media includes any available media that can beaccessed by the processor 50A. By way of example, computer readablemedia include computer readable storage media and computer readablecommunication media.

Computer readable storage media includes volatile and nonvolatile,removable and non-removable media implemented in any device configuredto store information such as computer readable instructions, datastructures, program modules or other data. Computer readable storagemedia includes, but is not limited to, random access memory, read onlymemory, electrically erasable programmable read only memory, flashmemory or other memory technology, compact disc read only memory,digital versatile disks or other optical storage, magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices,or any other medium that can be used to store the desired informationand that can be accessed by the processor 50A.

Computer readable communication media typically embodies computerreadable instructions, data structures, program modules or other data ina modulated data signal such as a carrier wave or other transportmechanism and includes any information delivery media. The term“modulated data signal” refers to a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, computer readable communication mediaincludes wired media such as a wired network or direct-wired connection,and wireless media such as acoustic, radio frequency, infrared, andother wireless media. Combinations of any of the above are also includedwithin the scope of computer readable media.

Electronic controller 50 is also shown as having a number of inputs andoutputs that may be used for implementing the operation of the flamelessheating system 10. One of the inputs is the measured leaving airflowtemperature provided by the temperature sensor T1. Another input is themeasured hydraulic fluid temperature in the storage tank 202 provided bytemperature sensor T2. Yet another input is the measured hydraulic fluidpressure upstream of the fourth valve 212 provided by pressure sensorP1. One skilled in the art will understand that many other inputs arepossible. For example, measured engine speed may be provide as a directinput into the electronic controller 50 or may be received from anotherportion of the control system via a control area network (CAN) 101. Themeasured pump displacement, for example via a displacement feedbacksensor, may also be provided. The operator user interface 52, which maybe electronic or electric, may also provide inputs into the controller,such as a temperature set point for the hydraulic fluid stored in thestorage tank 202.

As configured, the electronic controller 50 provides output commands tothe first valve actuator 206 a, the second valve actuator 208 a, thefourth valve actuator 212 a, and the fifth valve actuator 214 a. In oneembodiment, the valve command output from the controller 50 to eachvalve is a proportional signal.

The electronic controller 50 may also include a number of maps oralgorithms to correlate the inputs and outputs of the controller 50. Forexample, the controller 50 may include an algorithm to cooperativelycontrol the first valve 206 position and the fourth valve 212 positionbased on the measured temperature at temperature sensor T1 and/or thedesired flow rate for the airflow stream 32. An additional map may beprovided to correlate airflow volume with the hydraulic pressuremeasured at P1 and the commanded valve position for valve 212. In oneembodiment, the controller 50 includes an algorithm that provides upperand lower limits for the airflow stream airflow rate, the hydraulicsystem fluid pressure, and/or the hydraulic system temperature.

In one embodiment, the electronic controller has an automatic operationmode and a manual operation mode. In one embodiment, the automatic modeis engaged through the user interface 52, as shown in FIG. 2A. In theautomatic operation mode, the controller 50 places the first valve 206in a maximum pressure drop position, and also places the second andfifth valves 208, 214 in the closed position. The fourth valve 212 isthen modulated in a primary control loop to maintain a temperature setpoint at temperature sensor T1. As shown at FIG. 2A, the temperature setpoint for T1 can be designated by an operator through a user interface52 in communication with the controller 50. The automatic mode may alsoinclude limits on the position of the fourth valve 212 to ensure thatthe airflow rate is between an acceptable range of values. For example,the position of the valve 212 can be limited to ensure a minimum airflow rate of 1,000 cfm and a maximum air flow rate of 2,000 cfm. Asstated above, the airflow volume can be calculated by using existinginputs and command values in the controller 50. Alternatively, theairflow volume can be directly measured.

The manual mode allows an operator to optimize the operation of thesystem in cases where the automatic mode may provide less than desiredperformance. For example, it may be beneficial to override the systeminto the manual mode where additional airflow is needed for anapplication including a long ductwork run. In one embodiment, the manualmode is engaged through the user interface 52, as shown in FIG. 2B, andmay be implemented in a number of ways. For example, the controller 50and the user interface 52 can be configured to allow a user to manuallyset the position of the fourth valve 212. Referring to FIG. 2B, the userinterface 52 allows for the fourth valve 212 to be set anywhere betweena “Max Fan” position and a “Max Heat” position. The “Max Fan” positioncorresponds to the fourth valve 212 being placed in a condition wherethe maximum allowed hydraulic flow is sent to the hydraulic motor 216while the remaining hydraulic flow is sent to the first valve 206.Accordingly, this position places the system in a state where themaximum possible airflow is delivered from the system 10. The “Max Heat”position corresponds to the valve 212 being placed in a condition wherethe maximum allowed flow is sent to the first valve 206 while theremaining flow is sent to the hydraulic motor 216.

In either of the automatic or manual operational modes, the hydraulicfluid temperature T2 can be monitored by the controller 50 to ensure amaximum fluid temperature set point is not exceeded. The maximum fluidtemperature set point exists to protect the pump 204 and other hydrauliccomponents in the system 200 from damage caused by excessive fluidtemperatures. During operation of the system, it is possible that thefourth valve 212 will have fully moved to a position where maximum fluidis being delivered to the hydraulic motor 216 (i.e. minimum flow tovalve 206) and the fluid temperature at sensor T2 is still at or nearthe maximum fluid temperature set point. When such a condition exists,the controller 50 will begin modulating the first valve 206 to a moreopen position that will maintain the hydraulic fluid temperature at themaximum fluid temperature set point. Once the fluid temperature hasfallen back below the maximum fluid temperature set point, thecontroller 50 returns the first valve 206 to the maximum pressure dropposition and normal operation can resume.

The operation of the internal combustion engine 100 may be controlledthrough controller 50, through its own electronic controller 101, and/orthrough an electrical system. In one embodiment, the internal combustionengine 100 is operable at either a low rpm (e.g. 1,800 rpm) setting or ahigh rpm setting (e.g. 2,500 rpm) that are manually selectable by anoperator. In such a configuration, the low rpm setting is generally usedfor the warm-up and/or cool-down phases of operation while the high rpmsetting is utilized for normal heating operations in the manual orautomatic modes. In one embodiment, controls for selecting the rpmsetting are located on a panel separate from the user interface. In oneembodiment, the rpm controls are integrated into controller 50 and theuser interface.

During normal operation of the internal combustion engine 100, the pump204 will impart a torque load on the engine 100. This load is increasedas the first valve 206 moves towards the maximum pressure drop positionbecause the resistance in the hydraulic system 200 that the pump 204must work against is correspondingly increased. The hydraulic motor 216similarly increases the load on the engine 100. In order to maintain therpm setting as the torque load on the engine 100 increases, the engine100 will burn significantly more fuel as compared to an idle condition.As the engine is increasingly loaded and burns more fuel, heating intothe plenum 20 is also increased through increased engine radiation,increased heating load at the radiator 108, and increased exhaust outputthrough heat exchanger 120. In one embodiment, the engine 100, the firstvalve 206, and the hydraulic motor 216 are optimally selected such thatthe torque load and fuel consumption on the engine will be maximizedduring normal operation. Such a selection will result in a system 10that produces a maximum heating output for the size of the engine.

EXAMPLES

In one example of an optimized system, the flameless heating system 10can be configured to heat an ambient airflow stream 32 a from 0 degreesF. to 180 degrees F. at a volumetric flow rate of 1,200 cubic feet perminute. These conditions correspond to an overall heating output for theflameless heating system 10 of about 200,000 BTH/hour.

To achieve this output, a 1.5 liter diesel engine consuming about 1.8gallons of fuel per hour is selected. In this state, the engine 100 isproviding approximately 25 horsepower at a rotational speed of about2,500 rpm while radiating about 18,000 BTU/hour into the plenum 20.Additionally, the radiator 108 will add approximately 64,000 BTU/hour tothe plenum 20 under these conditions wherein the entering coolanttemperature is about 180 degrees F., the leaving coolant is about 170degrees F., and the coolant flow rate is about 14 gpm. Finally, theengine exhaust heat exchanger 120 will add approximately 26,000 BTU/hourwherein the entering exhaust temperature is about 800 degrees F. and theleaving temperature is about 500 degrees F.

Additionally, a pump 204 is selected that can provide about 28 gallonsper minute (gpm) of flow at a pressure of about 1,500 psi, whereinapproximately 5 gpm is delivered to the hydraulic motor 216 andapproximately 23 gpm of 200 degree F. fluid is delivered to the heatexchanger 220. In this state, heat exchanger 220 delivers about 92,000BTU/hour into plenum 20 with a fluid temperature drop of about 20degrees through the exchanger 220.

It is noted that the radiator 108 is located upstream of the heatexchanger 220 and the exhaust heat exchanger 120 because the radiator108 is operating at the lowest temperature of the three exchangers.Likewise, the exhaust heat exchanger 120 is located at the mostdownstream position due to this exchanger having the highesttemperatures. As the hydraulic heat exchanger 220 has an intermediatetemperature, the exchanger 220 is located between the radiator 108 andexhaust heat exchanger 120. By arranging the heat exchangers 108, 220,and 120 in this manner, the heating output of the system 10 can bemaximized.

When burning standard diesel fuel for the above described example, thetotal fuel consumption for the flameless heating system 10 isapproximately 260,000 BTU/hour. As the heating system provides about200,000 BTU/hour of usable heat via heated airflow stream 32 b, thetotal system efficiency is about 77%. This performance is significantlyhigher than many other types of flameless heating systems known in theart.

Table 1 below provides a design and performance summary of fourdifferently sized flameless heating systems 10 in accordance with theconcepts disclosed herein.

TABLE 1 System Engine Engine Engine Fuel Hydraulic Max BTU/hr PlatformHP RPM's Liter Rate (GPH) PSI Flow (GPM) CFM's Output Mule 25 2600 1.51.8 1500 28 1500 200,000 Small 43 2600 2.2 2.5 1600 30 4000 280,000Medium 73 2500 3.0 3.6 2500 40 5000 410,000 Large 113 2200 3.0 5.1 280058 6000 570,000

The various embodiments described above are provided by way ofillustration only and should not be construed to limit the claimsattached hereto. Those skilled in the art will readily recognize variousmodifications and changes that may be made without following the exampleembodiments and applications illustrated and described herein, andwithout departing from the true spirit and scope of the disclosure.

What is claimed is:
 1. A mobile heating system comprising: a. anenclosure supported by a mobile chassis, the enclosure defining an airplenum having an air inlet and an air outlet; b. a fan disposed in theair plenum, the fan being configured to move an air flow stream from theair inlet to the air outlet of the enclosure; c. an internal combustionengine disposed in the air plenum, the internal combustion engine havingan output shaft; and d. a hydraulic circuit including: i. a hydraulicpump operably coupled to the output shaft of the internal combustionengine; ii. a first heat exchanger located in the enclosure air plenumand in fluid communication with the hydraulic pump, the first heatexchanger being configured to transfer heat from fluid in the hydrauliccircuit to the air flow stream; iii. a hydraulic motor operably coupledto the fan, the hydraulic motor being in fluid communication with anddriven by the hydraulic pump; iv. a first valve disposed between thehydraulic pump and the heat exchanger, the first valve being configuredto resist fluid flow and to increase a fluid pumping pressure of thehydraulic pump; and v. a second valve upstream of the first valve, thesecond valve being configured to selectively direct hydraulic fluidbetween the first valve and the hydraulic motor.
 2. The mobile heatingsystem of claim 1, further comprising a control system configured tooperate the second valve to maintain a temperature set point of the airflow stream.
 3. The mobile heating system of claim 1, further comprisinga third valve upstream of the second valve, the third valve beingconfigured to bypass hydraulic fluid around the first and second valvesto the first heat exchanger.
 4. The mobile heating system of claim 3,further comprising a fourth valve in parallel with the first valve, thefourth valve being configured to bypass hydraulic fluid around the firstvalve to the first heat exchanger.
 5. The mobile heating system of claim4, wherein the first valve, the second valve, the third valve, and thefourth valve are provided in a single manifold block.
 6. The mobileheating system of claim 1, further comprising a second heat exchangerlocated in the enclosure air plenum, the second heat exchanger beingconfigured to transfer heat from an engine exhaust air stream to theheating air flow stream.
 7. The mobile heating system of claim 6,wherein the second heat exchanger includes a single tube having aplurality of offset straight sections.
 8. The mobile heating system ofclaim 1, further comprising a third heat exchanger located in theenclosure air plenum, the third heat exchanger being configured totransfer heat from an internal combustion engine coolant to the heatingair flow stream.
 9. The mobile heating system of claim 1, wherein theinternal combustion engine is controlled to maintain a generallyconstant rotational speed.
 10. The mobile heating system of claim 2,wherein the control system further includes a user interface.
 11. Themobile heating system of claim 10, wherein the user interface isconfigured to override the position of the first valve to a setposition.